It is well known that an initial guiding angle (pretilt angle) of liquid-crystal molecules needs to be determined by an alignment film in an LCD panel. The liquid-crystal molecules are aligned generally by means of a rubbing process for the alignment film. However, the rubbing process for the alignment film needs to be accurately controlled, but the operation of this technological process is not easy to control. Therefore, at present, a photo-alignment technique by using polymers has been proposed to overcome the drawback with respect to the above-mentioned rubbing alignment.
In general, reactive monomers need to be blended into an LC layer first, and then a voltage applying device is employed to apply a predetermined voltage to the LC layer in the photo-alignment technique. The LC layer is irradiated by ultraviolet (UV) light under the predetermined voltage. The reactive monomers are then polymerized and cured to form a polymer layer simultaneously on two opposite sides of the LC layer, so that the liquid-crystal molecules have a certain pretilt angle.
Referring to FIG. 1, FIG. 1 is a schematic drawing illustrating a conventional apparatus for applying curing voltages to a liquid crystal substrate. The liquid crystal substrate 10, which has a need for the photo-alignment process, is coupled to an external voltage applying device 20 via curing lines 122 and corresponding curing pads 124 outside a pixel region 120. Said applied predetermined voltage is transmitted to the pixel region 120 via the curing lines 122 by multiple probe pins 240 of a power supply 220 of the voltage applying device 20 electrically contacting the curing pads 124.
RGB signals are usually separated in the curing process, but the same voltages are fed via the probes 240. This can inspect more images in the following processes. However, the voltages of said fed RGB signals certainly have a subtle distinction due to a line resistance, machine accuracy, and other actual factors. When the voltages vary within a certain range, there is no influence on the panel to correctly display. But when the variation of the voltages is excessive, there is some difference in the pretilt angle of the liquid-crystal molecules due to the variation of the curing voltages, such that an abnormal display appears on subsequently displayed images. Moreover, because a person can not view the display of the panel inside a machine during the curing process, this abnormality can not be removed immediately.
In summary, there is a need to solve the problem of the poor alignment quality stemming from the variation of the curing voltages.